Writing an IMG File to Flash media
To write the USB IMG file to a Flash Card or USB pen drive you can do this with the Unix/Linux command dd:
dd if=<path_to/img_file.img> of=/dev/da0 bs=1m
Just substitute da0 with the device name of your USB stick.
NOTE: The USB images are FreeBSD-UFS formatted, and will not show up as a viewable file-system under Windows.
ADD SECTION ON how-to to flash a USB pen drive with the installer image. On Unix system this can be done with dd(1) and on Windows there's the  gui utility written by the M0n0wall crew.